1. Field of the Invention
This invention relates to hydrocarbon hydroprocessing catalysts, such as those utilized to catalyze the reaction of hydrogen with organonitrogen, organosulfur and organometallic compounds. More particularly this invention is directed to a catalyst useful for the hydrodesulfurization, hydrodenitrogenation and hydrodemetallation of hydrocarbon-containing feeds, such as residuum oils, and to a method for preparing such catalysts by employing an aqueous impregnating solution with porous, amorphous refractory oxide support particles.
2. Description of Prior Art
In the refining of hydrocarbons, it is often necessary to convert a hydrocarbon-containing oil fraction to different forms. Typically, particulate catalysts are utilized to promote desulfurization, denitrogenation or demetallization reactions when feedstocks such as residuum-containing oils are contacted with catalysts under conditions of elevated temperature and pressure and in the presence of hydrogen so that the sulfur components are converted to hydrogen sulfide, the nitrogen components to ammonia and the metals are deposited on the catalyst.
Hydroprocessing of hydrocarbon-containing oils may be carried out with a catalyst containing Group VIB and Group VIII hydrogenation metals on a refractory oxide support. Compositions containing these and other elements have been previously prepared by comulling and impregnation methods with supports with various pore size distributions.
Generally, such hydroprocessing catalysts having a substantial number of pores of diameter less than 120 angstroms have been effective for catalyzing desulfurization and denitrogenation reactions in residuum feedstocks, while catalysts having a substantial amount of pore volume in relatively larger pores (particularly pores of diameter greater than about 150 angstroms) have been effective for removal of contaminant metals (such as nickel and vanadium) from such feedstocks. In other words, hydroprocessing catalysts having larger sized pores have demonstrated greater effectiveness for demetallation of a residuum feedstock than catalysts of smaller sized pores and the two types of functions, i.e., demetallation and desulfurization, generally result in mutually exclusive pore sizes being preferred.
Examples of catalysts useful for hydroprocessing residuum-containing oils comprising a Group VIB metal, particularly molybdenum or tungsten, and a Group VIII metal, particularly cobalt or nickel, on an alumina base have been disclosed in U.S. Pat. Nos. 4,048,060, 3,509,044 and 4,460,707. The catalyst in U.S. Pat. No. 4,460,707 is disclosed to have excellent metals removal capacity and has an average pore diameter greater than about 180 angstroms and is prepared by impregnation, that is, by deposition of the active components on the support base by contact thereof with an aqueous solution containing the hydrogenation components in dissolved form. In U.S. Pat. No. 4,048,060 a catalyst having a relatively large average pore diameter between 140 and 190 angstroms is prepared by impregnating support materials containing minor amounts of silica, i.e., less than about 1.0 weight percent of silica with precursors of hydrogenation metals. Other alumina-containing catalysts disclosed in U.S. Pat. Nos. 4,048,060 as well as 3,509,044 contain about 1 to 6 weight percent of silica and have pore size distributions with a relatively small average pore diameter from 60 to 120 angstroms, and a maximum pore volume in pores of diameter from 30 to 70 angstroms, respectively.
Although conventional catalysts are active and stable for hydrocarbon hydroprocessing reactions, catalysts of yet higher activities and stabilities are still being sought. Increasing the activity of a catalyst increases the rate at which a chemical reaction proceeds under given conditions, and increasing the stability of a catalyst increases its resistance to deactivation, that is, the useful life of the catalyst is extended. In general, as the activity of catalyst is increased, the conditions required to produce a given end product, such as a hydrocarbon of given sulfur, nitrogen, and/or contaminant metals content, become more mild. Milder conditions require less energy to achieve the desired product, and catalyst life is extended due to such factors as lower coke formation or the deposition of less metals. The search continues for catalysts which are highly active for catalyzing both demetallation and desulfurization reactions during hydrocarbon hydroprocessing.